Descaling system for the cooling tubes of a steam condenser

ABSTRACT

A sponge ball type descaling system for cleaning the interior of the cooling water tubes of a steam condenser by conducting a large number of sponge balls therethrough, which comprises a sponge ball circulation passageway connected to the cooling water inlet and outlet pipes of the steam condenser; a sponge ball reservoir and a sponge ball circulation pump provided in the sponge ball circulation passageway; a vessel for wetting sponge balls with cooling water, thereby supplying fully water-soaked sponge balls to the descaling system, the water-soaking vessel and inlet and outlet valves thereof being arranged in a prescribed relationship with the sponge ball circulation passageway; and an evacuating device connected to the sponge ball-soaking vessel so as to evacuate the interior thereof to a prescribed extent and increase the water content of the sponge balls.

States Patent [1 1 Honma et all.

[4 1 Mar. 25, 1975 1 1 DESCALING SYSTEM FOR THE COOLING TUBES OF A STEAM CONDENSER [75] Inventors: Yoshio Honma, Yokosuka; Junichi Takahashi, Yokohama, both of Japan [22] Filed: Feb. 25, 1974 [21] Appl. No.: 445,581

[30] Foreign Application Priority Data 10/1964 Sebalo 12/1972 Takahashi 165/95 Primary Examiner-Manuel A. Antonakas Assistant Examiner-Daniel J. QConnor Attorney, Agent, or Firm-Oblon, Fisher, Spivak, McClelland & Maier [57] ABSTRACT A sponge ball type descaling system for cleaning the interiorof the cooling water tubes of a steam condenser by conducting a large number of sponge balls therethrough, which comprises a sponge ball circulation passageway connected to the cooling water inlet and outlet pipes of the steam condenser; a sponge ball reservoir and a sponge ball circulation pump provided in the sponge ball circulation passageway; a vessel for wetting sponge balls with cooling water, thereby supplying fully water-soaked sponge balls to the descaling system, the water-soaking vessel and inlet and outlet valves thereof being arranged in a prescribed relationship with the sponge ball circulation passageway; and an evacuating device connected to the sponge ballsoaking vessel so as to evacuate the interior thereof to a prescribed extent and increase the water content of the sponge balls.

4 Claims, 2 Drawing lFigures BACKGROUND OF THE INVENTION This invention relates to a descaling system for the heat-exchanging tubes of a heat exchanger, especially for the cooling tubes of a steam condenser and more particularly to the so-called sponge-ball type descaling system for removing substances deposited on the inner walls of the cooling water tubes of a steam condenser by continuously forcing a large number of watersoaked sponge balls through the cooling water tubes.

With such sponge-ball type descaling system, a sponge ball circulation passageway is connected to the cooling water inlet and outlet pipes of a steam condenser, and sponge balls are conducted through the cooling water tubes, using the force of cooling water streams running therethrough. This descaling system is adopted in, for example, a power plant. In recent years, various power plants use an automatic descaling system to save personnel requirement. Though the operation of the descaling system itself has been automated, sponge balls have still been treated manually. The treatment of sponge balls consists in deaerating sponge balls and soaking them with water before they are carried into the descaling system. The reason why sponge balls should be deaerated is that air-including sponge balls tend to float up to the surface of the cooling water and be unevenly distributed therethrough, failing to attain the uniform cleaning of the interior of the numerous cooling water tubes of a steam condenser. Hitherto, therefore, individual sponge balls have been manually deaerated and soaked with water.

SUMMARY OF THE INVENTION It is accordingly the object of this invention to provide a sponge ball type descaling system for the cooling water tubes of a steam condenser which comprises a sponge ball circulation passageway connected to the cooling water inlet and outlet pipes of the steam con denser; a sponge ball reservoir and a sponge ball circulation pump provided in the sponge ball circulation passageway; a vessel for soaking sponge balls with cooling water, thereby supplying fully Water-soaked sponge balls to the descaling system, the water-soaking vessel and the inlet and outlet valves thereof being arranged in a prescribed relationship with the sponge ball circu-' lation passageway; and an evacuating device connected to the sponge ball-soaking vessel so as to evacuate the interior thereof to a prescribed vacuum level.

The evacuating device connected to the sponge ballsoaking vessel consists of a vacuum pump or air ejector, a deaeration valve, etc. and is designed to deaerate sponge balls, thereby enabling them to be fully soaked with water.

Accordingly, the primary object of this invention is to provide a sponge ball type descaling system for the cooling water tubes of a steam condenser which can simultaneously effect both operations of deaerating all sponge balls and soaking them with water without the manual work of operators.

Another object of the invention is to provide an effective, inexpensive sponge ball type descaling system of simple construction and operation for the cooling water tubes of a steam condenser.

Other objects of the invention will be fully understood with reference to the appended drawings and description given in connection with the following preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows a schematic arrangement ofa descaling system accordingto the first embodiment of this invention for the cooling water tubes of a steam condenser; and

FIG. 2 illustrates a schematic arrangement of a descaling system according to the second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With regard to FIG. 1, referential numeral 1 denotes a steam condenser. The steam condenser 1 has a water box (inlet) 2 and a water box (outlet) 3 mounted on each side. A large number of cooling water tubes 4 are laid between the inlet and outlet water boxes 2, 3 so as to connect therewith at both ends. A cooling water feed pipe 5 is connected to the inlet water box 2 to supply cooling water, for example, sea water to the cooling water tubes supplied by a cooling water circulation pump (not shown). A cooling water discharge pipe 6 is connected to the outlet water box 3 to drain off the used cooling water. Provided at a suitable intermediate point on the cooling water outlet pipe 6 is the later described collector 7 for catching only descaling-sponge balls. The descaling system of this invention for the cooling water tubes of a steam condenser including the collector 7 is installed between the cooling water inlet and outlet pipes 5, 6.

A sponge ball circulation passageway 8 is formed between the collector 7 and the cooling water feed pipe 5. Fitted to both ends of the sponge ball circulation passageway 8 are the valves 9, 10 which are closed when the descaling system is out of operation. In other words, the closed condition of the valves, 9, 10 means the normal operation of the steam condenser 1. At this time, cooling water is pumped up, from the sea, conducted through the feed pipe 5, inlet water box 2, cooling tubes 4, outlet water box 3 and discharge pipe 6 in turn and finally return into the sea, and consequently is prevented from running into the sponge ball circulation passageway 8.

Located substantially at the center of the sponge ball circulation passageway 8 is a sponge ball water-soaking vessel 11. This water-soaking vessel 11 assumes a sufficiently large hopper shape to hold all sponge balls 12 required to descale the inner walls of the cooling water tubes 4 of the steam condenser I. A wire net 13 is mounted on part of the upper surface of the watersoaking vessel 11. The wire net 13 has meshes just small enough to prevent sponge balls 12 from being thrown out of the water-soaking vessel 11. The remaining portion of the upper surface of the water-soaking vessel 11 is fitted with a closure (not shown) which is opened only when used sponge balls 12 are replaced by fresh ones, but normally closed. Provided on the wire net 13 is a float valve 14 which is connected to the later described evacuating device 15 for evacuating the interior of the watersoaking vessel, and the evacuating de vice 15 consists of components surrounded with dotdash lines shown in FIG. 1.

The inlet valve 16 and outlet valve 17 of the watersoaking vessel 11 are provided on the sponge ball circulation passageway 8. Both valves 16, 17 are motor actuated ones whose operation is automatically regulated by remote control. Located between the inlet valve 16 and valve are a check valve 18 and a sponge ball circulation pump 19. The check valve 18 allows cooling water to flow through the sponge ball circulation passageway 8 only in one direction from the right to the left of FIG. 1 but prevents it from running in the opposite direction. The drive of the sponge ball circulation pump 19 which is automatically regulated by remote control causes sponge balls 12 in the watersoaking vessel 11 to be compulsorily transferred together with cooling water from the sponge ball circulation passageway 8 to the cooling water feed pipe 5. A sponge ball reservior 20 is provided in the sponge ball circulation passageway 8 between the outlet valve 17 of the watersoaking vessel 11 and the valve 9. While one cycle of descaling operation is continued, the sponge ball reservior 20 is put out of operation, allowing sponge balls to pass therethrough. Upon completion of one cycle of descaling operation, all used sponge balls 12 are collected in the reservior 20 and thereafter taken out of the descaling system.

A deaeration pipe 21 led in the evacuating device 15 has one end connected to the float valve 14 and the other end divided into two branch pipes, one of which is open to the atmosphere through a deaeration valve 22 and the other of which connects to a cooling water separator 24 through another deaeration valve 23. The cooling water separator 24 is connected to one end of a second deaeration pipe 25 which is provided with a deaeration valve 26 and filter 27, and further downstream to a vacuum pump 28. The vacuum pump 28 may be replaced by an ordinary air extracting means, for example, an air ejector.

There will now be described the operation of a descaling system according to the first embodiment of this invention for the cooling water tubes of a steam condenser.

First, all required sponge balls 12 are received in the sponge ball water-soaking vessel 11. At this time, the inlet valve 16 of the water-soaking vessel 11 remains closed, while the outlet valve 17 thereof is left open. The valves 9, 10 are opened in advance. When a re quired number of sponge balls 12 have all been received in the water-soaking vessel 11, the evacuating device 15 is actuated after the outlet valve 17 is closed. Actuation of the evacuating device 15 increasingly evacuates the interior of the water-soaking vessel 11 to deaerate the sponge balls 12. During this operation, the sponge balls 12 are prevented by the wire net 13 from being thrown out of the water-wetting vessel 11 toward the deaeration pipe 21 under any vacuum conditions.

When the water-soaking vessel 11 has been evacuated to a prescribed vacuum level, the inlet valve 16 is opened. Accordingly, cooling water is led from the discharge pipe 6 through the collector 7 to the sponge ball circulation passageway 8 and then to the water-soaking vessel 11 to soak the sponge balls 12 received therein with water. When the water-soaking vessel 11 is fully filled with cooling water, the inlet valve 16 is closed, the vacuum pump 28 is actuated, the deaeration valves 23, 26 remain open and the air contained'in the coolingwater is extracted (Deaeration valve 22 remains closed) by the pump 28 through the separator 24 and the filter 27.

This evacuating operation causes air to be transferred together with cooling water to the first deaeration pipe 21 and also the cooling water itself to be substantially separated from air by the separator 24. The cooling water which has not been fully separated further flows in the form of mist together with air to the second deaeration pipe 25. However, the misty cooling water is completely eliminated by the filter 27, and

consequently air alone is led to the vacuum pump 28,.

thereby saving the pump 28 from the harmful effect of cooling water. If the vacuum pump 28 itself is provided with a device for preventing the ingress of cooling water, the separator 24 and filter 27 will be unnecessary.

After this operation is continued for a while, the vacuum pump 28 is stopped, the valves 23, 26 are closed and the valve 22 is opened to soak the sponge balls 12 fully with cooling water under atmospheric pressure. After this process, the sponge ball circulation pump 19 is driven, and the inlet valve 16 and outlet valve 17 are opened. The fully soaked spong balls in the watersoaking vessel 11 are forced into the circulation passageway 8 by the discharge pressure of the circulation pump 19 and pass through the sponge ball reservoir 20 into the cooling water inlet pipe 5.

When the sponge ball circulation pump 19 is driven, the air unavoidably introduced from the outside through the base portion of the pump 19 is collected in the water-soaking vessel 11, but is released automatically through the floot valve 14 into the atmosphereby leaving open the deaeration valve 22.

Sponge balls 12 brought into the cooling water feed pipe 5 are transferred together with cooling water into the inlet water box 2 andthen into the cooling water tubes 4 of the steam condenser 1. The sponge balls 12 already fully soaked with water are prevented from floating upward in the inlet water box 2 and consequently uniformly distributed through the cooling water tubes 4. While passing through the cooling water tubes 4, the sponge balls 12 are carried onwards while rubbing off injurious deposits on the inner walls of the cooling water tubes 4, collected in the outlet water box 3, and then drained into the discharge pipe 6. After transferred through the discharge pipe 6, the sponge balls 12 are returned through the collector 7 to the circulation passageway 8. Most of the cooling water is drained off, for example, into the sea immediately from the discharge pipe 6. However, part of the cooling water flows into the circulation passageway 8 to push the sponge balls 12 thereinto. The desired descaling operation of the cooling water tubes 4 of the steam condenser 1 can be fully attained by repeating the circulation of numerous sponge balls 12 for 30 minutes or an hour at the rate of once every 30 seconds.

After the finish of the descaling operation, the sponge balls 12 are soiled, broken or have the diameter decreased as the result of repeatedly taking part in scraping off deposits on the inner walls of the cooling tubes 4. These defective sponge balls 12 are all collected in the sponge ball reservoir 20 finally to be removed to the outside. When the sponge ball circulation pump 19 is stopped with the valves 9, 10 closed, then the descaling system is brought to an condition out of operation. The succeeding cleaning of the inner walls of the cooling water tubes 4 of a steam condenser l is carried out by putting fresh sponge balls 12 in the water-soaking vessel 11.

The operation of descaling the inner walls of the cooling water tubes 4 of a steam condenser l by the descaling system according to the first embodiment of this invention can be automatically carried out by regulating the operation time and timing of the associated valves and pumps through automatic sequence control. Particularly applied for the sequence control are the inlet and outlet valves 16, 17, deaeration valves 22, 23, 26, sponge ball circulation pump 19 and vacuum pump 28.

Further, it is possible to provide the collector 7 with a supervisory means for detecting the extent to which circulating sponge balls 12 are soiled and, when soiling reaches a prescribed extent, automatically stop the sponge ball circulation pump 19.

FIG. 2 illustrate a descaling system according to the second embodiment of this invention for the cooling water tubes lof a steam condenser 1. The components of FIG. 2 the same as those of FIGv 1 are denoted by the same numerals. There will now be described only the different arrangement of FIG. 2 from that of FIG. 1.

Inlet and outlet pipes 29, 30 respectively provided with inlet and outlet valves 16, 17 are connected at one end to the both inlet and outlet sides of the sponge ball water-soaking vessel 11 for leading numerous sponge balls 12. The inlet and outlet pipes 29, 30 are con nected at the opposite end to the sponge ball circulation passageway 8. In the second embodiment, there fore, the sponge ball water-soaking vessel 11 is arranged parallel to the sponge ball circulation passageway 8, while, in the first embodiment, the watersoaking vessel 11 is connected in series to the sponge ball circulation passageway 8. The embodiment of FIG. 2 has the same arrangement as that of FIG. 1 in that the circulation passageway 8 is connected at one end directly to the cooling water feed pipe 5 and also to the cooling water discharge pipe 6 at the other end through the sponge ball collector 7. According to the second embodiment of FIG. 2, the sponge ball circulation passageway fi further has the sponge ball reservoir 20 provided with an inlet valve 31 and the circulation pump 19 provided with an inlet valve 32. The upstream end of the inlet pipe 29 of the sponge ball water-soaking vessel 11 is connected to the passageway 8 between the inlet valve 31 of the sponge ball reservoir 20 and the check valve 18 on the upstream side of the inlet valve 31. The downstream end of the outlet pipe 30 of the sponge ball water-soaking vessel 11 is connected between the valve 10 and the inlet valve 32 of the circulation pump 19 on the upstream side ofthe inlet valve 32. Mounted on part of the upper surface of the sponge ball water-soaking vessel 11 is the wire net 13, on which the float valve 14 is provided. The water-soaking vessel 11 is connected to the evacuating device 15 through the float valve 14. This arrangement, as well as that of the evacuating device 15 itself, is the same as in the first embodiment.

There will now be described the descaling operation of the second embodiment by means of sponge balls. The sponge ball water-soaking vessel 11 filled with sponge balls is evacuated to a prescribed vacuum level, with the inlet and outlet valves 16, 17 closed, by actuating the vacuum pump 28 as in the first embodiment. Thereafter, the valves 10, 32 closed up to this point are opened, and the inlet valve 16 of the sponge ball watersoaking vessel 11 is opened with the inlet valve 31 of the sponge ball reservoir closed. Accordingly, cooling water is brought into the water-soaking vessel 11 through the sponge ball circulation passageway 8 and the inlet pipe 29 of the vessel 11 to fill the watersoaking vessel 11 with cooling water. When the watersoaking vessel 11 is fully filled with water, the inlet valve 16 is closed and the deaeration valve 22 is opened to apply atmospheric pressure to the interior of the water-soaking vessel 11 after the same process as in the first embodiment, thereby enabling the sponge balls 12 to be fully soaked with cooling water. When the sponge ball circulation pump 19 is driven with the inlet valve 16 and the outlet valve 17 opened and the inlet valve 31 of the sponge ball reservoir 20 and the valve 9 are opened, then the sponge balls 12 which have been fully deaerated and soaked with cooling water are all compulsorily drawn off together with cooling water from the water-soaking vessel 11 into the circulation passageway 8 through the outlet pipe 30 and the sponge balls 12 now carried into the circulation passageway 8 are further transferred to the cooling water feed pipe 5 by the action of the circulation pump 19. After the all sponge balls were transferred into the cooling water inlet pipe 5 the inlet and the outlet valves 16, 17 are closed. Thereafter, as in the first embodiment, the inner walls of the cooling water tubes 4 of the steam condenser 1 are cyclically descaled by the sponge balls 12, During this descaling operation, the inlet and outlet valves 16, 17 remain closed to prevent the sponge balls 12 from being brought back into the water-soaking vessel 11 to keep it empty of the balls. Therefore, the sec ond embodiment enables fresh sponge balls to be supplied to the descaling system while the cleaning operation is still'going on. The second embodiment has the advantage that the water-soaking vessel can be designed to have a small capacity. Namely, even where a desired descaling effect is not attained simply by circulating as many sponge balls as can be received in the water-soaking vessel atone time, descaling operation can be efficiently carried out without the shutdown of a descaling system by continuously supplying fresh sponge balls to the vessel. Accordingly, application of a small-capacity water-soaking vessel which has now been made possible by this invention has an exceeded effect of rendering an entire descaling system compact with the resultant decrease of manufacturing cost.

When, as in the first embodiment, the evacuating de vice 15 is actuated after fresh sponge balls 12 are put in the water-soaking vessel 11 and thereafter the inlet valve 16 thereof is opened, then part of the cooling water is led into the inlet pipe 29 of the water-soating vessel 11 from the sponge ball circulation passageway 8 and then into the water-soaking vessel 11 from the inlet pipe 29, thereby soaking sponge balls 12 with cooling water in the same manner as described above. When the inlet and outlet valves 16, 17 are opened after the sponge balls are fully filled with water by the water-soaking vessel 11,.then the fresh sponge balls 12 are all forced into the circulation passageway 8, thereby contributing to the descaling'operation in cooperation with the previously charged sponge balls 12.

The descaling operation of the second embodiment is regulated by automatic sequence control as in the first embodiment.

As mentioned above, the descaling system of this invention enables the sponge balls to be automatically deaerated and soaked with water at the same time and also the regulation of their circulation to be attained by the automatic sequence control by valves and pumps, thereby attaining a quicker descaling operation, and

more saving personnel requirement and cost than the prior art descaling system in which operators manually treated sponge balls one after another. Moreover, the descaling system of the invention is of sufficiently simple construction and operation to admit of easy inspection and maintenance.

Obviously, this invention is not limited to the first and second embodiments. For example, the water-soaking vessel, circulation pump and reservoir included in the sponge ball circulation system may be arranged in any other relationship than described in the foregoing embodiments. It is also possible to provide a single vessel capable of concurrently acting as a sponge ball watersoaking vessel and receptacle, instead of installing these components separately as described herein.

What we claim is:

l. A descaling system for cleaning the inner walls of the cooling water tubes of a steam condenser by a plurality of sponge balls which comprises a cooling water feed pipe connected to the inlet side of the cooling water tubes to supply cooling water thereto; a cooling water discharge pipe connected to the outlet side of the cooling water tubes to drain off cooling water therefrom; a sponge ball collector provided on the discharge pipe; a sponge ball circulation passageway connected at one end to the cooling water feed pipe and at the other end to the collector, the circulation passageway containing a sponge ball circulation pump and a sponge ball reservoir; a sponge ball water-soaking vessel for receiving a plurality of sponge balls to soak them with cooling water; an inlet valve for the water-soaking vessel so as to supply cooling water thereto from the sponge ball circulation passageway or stopping the supply; an outlet valve for the water-soaking vessel so as to drain off cooling water and the sponge balls contained therein to the circulation passageway or shutting off the passage of the cooling water and sponge balls; an evacuating device connected to the water-soaking vessel for holding sponge balls to deaerate its interior, thereby attaining evacuation to a prescribed vacuum level, wherein, when the sponge ball water-soaking vessel is evacuated to a prescribed vacuum level by the evacuating device, the inlet valve of the sponge ball water-soaking vessel is opened to lead cooling water thereinto from the sponge ball circulation passageway, thereby soaking the sponge balls received in the watersoaking vessel with cooling water.

2. A descaling system according to claim 1, wherein a wire net is mounted on part of the upper surface of the sponge ball water-soaking vessel to prevent sponge balls received therein from being thrown outside; a float valve is provided on the wire net; and the watersoaking vessel is connected to the evacuating device through the wire net and float valve.

3. A descaling system according to claim 1, wherein the evacuating device comprises a first deaeration pipe having one end connected to the sponge ball watersoaking vessel and the other end divided into two branches; :1 deaeration valve provided on one of the branches of the first deaeration pipe to cause, when opened, the interior of the water-soaking vessel to connect with the atmosphere; a cooling water separator positioned on the other branch of the first deaeration pipe to separate cooling water from air; a second deaeration pipe connected at one end to the cooling water separator; a filter provided in the second deaeration pipe to eliminate misty cooling water contained in the air transferred from the cooling water separator to the second deaeration pipe; a deaeration means located in the second deaeration pipe behind the filter; and a deaeration valve fitted to either or both of the other branch of the first deaeration pipe and the second deaeration pipe.

4. A descaling system for cleaning the inner walls of the cooling water tubes ofa steam condenser by a plurality of sponge balls which comprises a cooling water feed pipe connected to the inlet side of the cooling water tubes to supply cooling water thereto; a cooling water discharge pipe connected to the outlet side of the cooling water tubes to drain off cooling water therefrom; a sponge ball collector fitted to the discharge pipe; a sponge ball circulation passageway connected at one end to the cooling water feed pipe and at the other end to the sponge ball collector, said circulation passageway containing a sponge ball circulation pump and reservoir; a sponge ball water-soaking vessel for receiving a plurality of sponge balls to soak them with cooling water; a soaking vessel inlet pipe for connecting the inlet side of the soaking vessel to the circulation passageway; a soaking vessel outlet pipe for connecting the outlet side of the soaking vessel to the circulation passageway; an inlet valve fitted to the soaking vessel inlet pipe; an outlet valve provided on the soaking vessel outlet pipe; and evacuating device connected to the water-soaking vessel for holding sponge balls to deaerate the interior of the water-soaking vessel for evacuation, wherein, when the interior of the water soaking vessel is evacuated to a prescribed vacuum level by the evacuating device, the inlet valve of the water-soaking vessel is opened to lead cooling water thereinto from the sponge ball circulation passageway through the inlet pipe of the water-soaking vessel to soak the sponge balls with cooling water; and when the sponge balls are fully filled with water, the outlet valve of the water-soaking vessel is opened to transfer all the sponge balls to the circulation passageway through the outlet pipe of the water-soaking vessel. 

1. A descaling system for cleaning the inner walls of the cooling water tubes of a steam condenser by a plurality of sponge balls which comprises a cooling water feed pipe connected to the inlet side of the cooling water tubes to supply cooling water thereto; a cooling water discharge pipe connected to the outlet side of the cooling water tubes to drain off cooling water therefrom; a sponge ball collector provided on the discharge pipe; a sponge ball circulation passageway connected at one end to the cooling water feed pipe and at the other end to the collector, the circulation passageway containing a sponge ball circulation pump and a sponge ball reservoir; a sponge ball water-soaking vessel for receiving a plurality of sponge balls to soak them with cooling water; an inlet valve for the watersoaking vessel so as to supply cooling water thereto from the sponge ball circulation passageway or stopping the supply; an outlet valve for the water-soaking vessEl so as to drain off cooling water and the sponge balls contained therein to the circulation passageway or shutting off the passage of the cooling water and sponge balls; an evacuating device connected to the water-soaking vessel for holding sponge balls to deaerate its interior, thereby attaining evacuation to a prescribed vacuum level, wherein, when the sponge ball water-soaking vessel is evacuated to a prescribed vacuum level by the evacuating device, the inlet valve of the sponge ball water-soaking vessel is opened to lead cooling water thereinto from the sponge ball circulation passageway, thereby soaking the sponge balls received in the water-soaking vessel with cooling water.
 2. A descaling system according to claim 1, wherein a wire net is mounted on part of the upper surface of the sponge ball water-soaking vessel to prevent sponge balls received therein from being thrown outside; a float valve is provided on the wire net; and the water-soaking vessel is connected to the evacuating device through the wire net and float valve.
 3. A descaling system according to claim 1, wherein the evacuating device comprises a first deaeration pipe having one end connected to the sponge ball water-soaking vessel and the other end divided into two branches; a deaeration valve provided on one of the branches of the first deaeration pipe to cause, when opened, the interior of the water-soaking vessel to connect with the atmosphere; a cooling water separator positioned on the other branch of the first deaeration pipe to separate cooling water from air; a second deaeration pipe connected at one end to the cooling water separator; a filter provided in the second deaeration pipe to eliminate misty cooling water contained in the air transferred from the cooling water separator to the second deaeration pipe; a deaeration means located in the second deaeration pipe behind the filter; and a deaeration valve fitted to either or both of the other branch of the first deaeration pipe and the second deaeration pipe.
 4. A descaling system for cleaning the inner walls of the cooling water tubes of a steam condenser by a plurality of sponge balls which comprises a cooling water feed pipe connected to the inlet side of the cooling water tubes to supply cooling water thereto; a cooling water discharge pipe connected to the outlet side of the cooling water tubes to drain off cooling water therefrom; a sponge ball collector fitted to the discharge pipe; a sponge ball circulation passageway connected at one end to the cooling water feed pipe and at the other end to the sponge ball collector, said circulation passageway containing a sponge ball circulation pump and reservoir; a sponge ball water-soaking vessel for receiving a plurality of sponge balls to soak them with cooling water; a soaking vessel inlet pipe for connecting the inlet side of the soaking vessel to the circulation passageway; a soaking vessel outlet pipe for connecting the outlet side of the soaking vessel to the circulation passageway; an inlet valve fitted to the soaking vessel inlet pipe; an outlet valve provided on the soaking vessel outlet pipe; and evacuating device connected to the water-soaking vessel for holding sponge balls to deaerate the interior of the water-soaking vessel for evacuation, wherein, when the interior of the water soaking vessel is evacuated to a prescribed vacuum level by the evacuating device, the inlet valve of the water-soaking vessel is opened to lead cooling water thereinto from the sponge ball circulation passageway through the inlet pipe of the water-soaking vessel to soak the sponge balls with cooling water; and when the sponge balls are fully filled with water, the outlet valve of the water-soaking vessel is opened to transfer all the sponge balls to the circulation passageway through the outlet pipe of the water-soaking vessel. 